1. Field of the Invention
The present invention relates to an imaging apparatus and an imaging method for photographing an object to be inspected.
2. Description of the Related Art
In recent years, an apparatus using optical coherence tomography (OCT) for acquiring a tomographic image by using interference of low-coherence light (hereinafter also referred to as “OCT apparatus”) has been put into practical use. The OCT is exemplified in a document tiled as “Real-time evaluation of retinal blood flow with ultrafast acquisition by color Doppler Fourier domain optical coherence tomography” in OPTICS EXPRESS 2003 Vol. 11, No. 23 P 3113-3121. The apparatus allows a tomographic image to be acquired with a resolution as high as that of a wavelength of light entering an object to be inspected. Therefore, the tomographic image of the object to be inspected can be acquired with a high resolution. The OCT apparatus is particularly useful as a fundus examination apparatus for acquiring a tomographic image of a retina located at the back or fundus of an eye.
On the other hand, the OCT apparatus is generally based on two-dimensional scanning, and therefore has relatively long photographing time. Further, the OCT apparatus constructs the tomographic image from interference light between measuring light and reference light described later. Therefore, in order to adjust an interference-light intensity in accordance with a state of the apparatus such as a transmittance of an optical system and reflection by the object to be inspected, an adjustable neutral density filter is sometimes required to be inserted into an optical path of the reference light so as to perform adjustment in accordance with the interference-light intensity or the like.
Further, in the case where the apparatus has been used over a long period of time, a transmitted-light amount sometimes changes depending on a light amount from a light source, fine dust in an optical path, a change in coating on a lens, and the like. Also when the apparatus is used over a long period of time, the adjustment of a reference-light amount is sometimes required. The reason why the reference light is adjusted is as follows. The interference intensity can be changed by both the reference-light intensity and the measuring-light intensity. However, changing the measuring-light intensity means a change in the amount of light illuminated on the object to be inspected. Therefore, when there are restrictions on an illuminated-light amount both in terms of safety and in terms of image quality, the interference intensity is adjusted by adjusting the reference-light amount.
The adjustment described above can be experimentally implemented appropriately while a state of the apparatus is checked. However, if an inspector performs imaging after checking the state of the apparatus and implementing the adjustment, a long time is required in total, which becomes a burden on a subject.